Preliminary results show that when reconstituted with specific thylakoid lipids, purified spinach LHC-II forms 2-D particle arrays in a square lattice resembling the organization of photosystem II arrays seen in freeze-fractured thylakoid membranes. Ths contrasts with the hexagonal LHC-ll arrays described and crystallographicaily resolved by W. Kuehlbrandt. The influence of lipid composition and illumination will be explored.